iMac 2011 HD Thermal Sensor

After replacing a few 2010 iMac Seagate hard drives, I came across a few 2011 iMacs that did not have and external temperature sensor, or a wire pair going directly to the hard drives. I figured that they simply did not require a sensor or were getting the temperature from some other source, so I replaced the hard drives in a few. The fans ran at full blast. I could not figure out where the sensor was until reading a few pages into an Anandtech article on the 2011 iMacs. The sensor is once again provided by special firmware on Apple drives but these are wired through the SATA power connector.

The article explains that one the SATA power connector, pins 2 and 7 are carrying the temperature data. The problem is that the pins 2 and 7 referenced are being read on the motherboard side of the connector not the SATA power connector. I ended up having to dismantle an iMac to find those pins on the motherboard and trace them to the wires going into the SATA power connector. As it turns out, the two pins are the first wire and the fourth wire reading from the SATA power connector key side. Clipping those and soldering them together makes the iMac happy.

Clemens Leu

May 12, 2016

Many thanks Matt for this IMPORTANT information, - I almost cut the wrong wires (2 & 7).
Thanks to this blog it is now clear that at the SATA side of the cable the wires 1 and 4 had to be shorted. Furthermore, this solution is also much faster then Apple's official one, - the iMac does not have to be taken fully apart.
My successfully modded 2011 21,5 iMac works quiet again and thanks to the Crucial MX200 500GB SSD super fast. :) Really great!

Charles

September 19, 2017

Hi, does doing this have an impact on cooling performance? Does the hard drive fan ramp up and down as needed when temp's rise and fall? I'm curious to know what this actually does in terms of what data is being sent to the logicboard.
Thanks...

Charles

September 19, 2017

Just as an addition... assuming there is no temp going back the logicboard and the fan just runs at default speed..... rather than solder together the two wires. Could you solder in a 2N3904 transistor to the two snipped cables?